The present invention relates to dust separators and collectors commonly used by wood workers to separate and collect debris composed of particulates such as sawdust and shavings created by debris sources; i.e. power tools such as saws, sanders, jointers, routers, etc. Certain types of dust collectors generally comprise two chambers having an opening therebetween. The first chamber functions to separate the debris from an airflow created by a vacuum source such as a shop-vac. The second chamber, which is situated below the first chamber, collects the debris that falls by gravity therein through the opening. Dust collectors are situated between the debris source and the vacuum source and function to remove as much of the debris as possible before it enters the vacuum source. This retards clogging of the vacuum's filter, necessitating its replacement or cleaning less often. The reduced clogging also permits the vacuum source to operate more efficiently for a longer time.
The first chamber is typically circular in cross-section and comprises cylindrical or funnel-shaped sidewalls. The first chamber also includes an input port and an output port. The input port comprises an inlet and connects a first conduit to the debris source. The output port, which is centrally situated at the top of the first chamber, comprises an outlet and connects a second conduit to the vacuum source. In these devices, air and debris are drawn into the first chamber through the inlet by suction created at the outlet. The input port is positioned laterally with respect to the output port and is oriented such that the airflow is drawn into the first chamber in a tangential, cyclonic manner. The opening at the bottom of the first chamber has a cross-sectional area that is significantly smaller than the cross-sectional area of the second chamber. Accordingly, airflow velocity and turbulence decreases dramatically below the opening and the debris that falls therethrough tends to slow and settle into the second chamber. This also reduces the tendency of the debris in the second chamber to re-enter the first chamber. In some devices, the opening is an annular space around a skirt or baffle at the bottom of the first chamber. In another device it is simply a centrally situated round opening at the bottom of a funnel-shaped first chamber.
In some prior-art devices, the inlet is positioned above the outlet. Consequently, the airflow and debris spiral downward along the first chamber's sidewall toward the outlet. In other devices the inlet and outlet are substantially on the same plane whereby incoming the airflow and debris initially follow a substantially circular path. In any case, the airborne debris is centrifugally forced to the sidewall and travels along a path dictated by the sidewall's contour, the airflow direction, and gravity. The airflow below the outlet then becomes a vortex that spirals inward and upward toward the outlet. Accordingly, any downward movement of the debris caused by airflow essentially ceases below the outlet. These devices must rely solely on the force of gravity for the final movement of the debris through the opening. Since the debris is often comprised of small particulates of low specific gravity, some will dwell in the vortex for sufficient time that it is drawn into the outlet.
Since prior-art devices, and the present invention, relate to the physics of objects striking and sliding on surfaces, the following must be understood: The path of an object before and after striking a flat surface will be on a plane that is perpendicular to the flat surface. And when an airborne object strikes a curved surface it will follow a path along a plane that is perpendicular to a plane tangent to the curved surface at the point of contact. This is true even in the case of conical, spherical or other compound-curved surfaces. And when an object slides on an inwardly curving surface it is acted on by centripetal forces normal to a plane tangent to the surface whereat the object presently exists. The path of the object is accordingly dictated by these centripetal forces. Simply put, objects sliding on surfaces will follow the path of least resistance.
There is disclosed in U.S. Pat. No. 7,282,074 (Witter) a dust-collecting device comprising a funnel-shaped first chamber having a downwardly reducing diameter, and a cylindrical second chamber. The first chamber; has an output port centrally positioned at its top; an input port tangentially oriented on its side adjacent the top; and a centrally positioned opening at the bottom that communicates with the second chamber. The output port comprises a conduit that protrudes downward into the first chamber to approximately two-thirds the chamber's depth and has an outlet thereat. In use, the incoming airflow and debris are caused by suction at the outlet to spiral downward along the conical sidewall of the first chamber from the inlet toward the outlet. As discussed above in the comments about the physics of objects striking and sliding on curved surfaces, the debris must overcome its tendency to spiral upward as it travels along the funnel-shaped sidewalls. In the portion above the outlet, the combined forces of the air current and gravity overcome this tendency. However, adjacent and below the outlet any downward movement of the air ceases and any subsequent downward movement of the debris is solely due to gravity. In fact, the funnel shape of the first chamber not only inhibits downward movement of the debris, it conveys the debris close to the outlet where some is likely to be drawn therein and not passed on to the second chamber.
Another device described in U.S. Pat. No. 7,128,770 (Oh, et al.) discloses a cyclone type dust collector that basically comprises four chambers. The first chamber is cylindrical in form and includes: a tangential oriented input port having an inlet disposed on its upper surface adjacent its cylindrical wall for the incoming air and debris; a cylindrical first output port centrally positioned on its upper surface and having solid walls at its upper portion and a first outlet comprising a grill having perforations around its lower portion. The perforations are for allowing the passage of small particulates, while preventing larger particulates from exiting through the first outlet to the third chamber; and, a skirt at the bottom of the lower portion defining an annular space between the skirt and the cylindrical walls of the first chamber through which the larger particulates may pass to the second chamber. The skirt also comprises a declining upper surface that terminates at a cutout part through which even larger particulates may fall into the second chamber. The second chamber is for collecting the particulates separated from the first chamber. The third chamber comprises an annular array of cones that cyclonically separate and collect the fine particulate material entering through the grill from the first chamber. The fourth chamber comprises a second output port for connecting to a vacuum source. Essentially, the device first separates the larger particulate mater in the first chamber and then removes the finer matter in the third chamber.
The inlet to the first chamber is the terminal opening of a gradually lowering air guide wall that communicates to a debris source. Therefore, as the debris enters the first chamber it is initially directed somewhat downwardly in a circular path around the upper, solid-walled upper portion of the first output port. The continued downward spiral of the debris is caused by the suction through the perforations on the lower portion. As is typical of cyclone type dust collectors, and in accordance with the laws of fluid dynamics, the debris-borne airflow of Oh's device slows as it enters the large cross-sectional space of the first chamber through the smaller cross-sectional opening of the inlet. Accordingly, the airborne-debris travels downward guided by the chamber's cylindrical walls in a spiraling path around the solid-walled upper portion at this reduced rate. As it circles the lower perforated portion, literally all of the air and some of the debris pass through the perforations in route to the vacuum source. Due to the relatively large height and diameter of the lower perforated portion the debris is subject to being drawn through the perforations for a relatively long time and distance. Consequently, as intended, some of the finer particulates are drawn in through the perforations. And the fact that a grill is incorporated at all suggests it is expected even some of the larger particulates will also be drawn thereto. In which case clogging of the perforations could occur which would reduce the efficiency of the grill and therefore, the device. Since all of the incoming air passes through the grill, plus the fact that the walls of the first chamber are cylindrical, any downward bias to the debris flow caused by the suction through the grill literally ceases at the lower end of the grill. Therefore, the circling particulate matter that evades entering the grill relies entirely on gravity to fall through the annular opening into the second chamber.
It is apparent the geometries and proximities of the key elements of first and second chambers of Oh's device simply do not effect sufficient removal of debris, and that the device relies on the third chamber to complete the job. Although Oh's device may function to remove a large percentage of the particulate matter from the incoming airflow, it does have certain drawbacks. Primarily, it is quite complicated and has many parts that would be expensive to produce and assemble. It also has a multitude of small spaces and crevices where dust may accumulate that would be difficult to access and clean.
And another device for separating and collecting debris from airflow is disclosed in U.S. patent application Ser. No. 12/624,022 (Thien). This device comprises a first chamber that removes debris from incoming airflow and is situated above a second chamber that collects the debris. A substantially cylindrical vessel such as a pail or trashcan is provided that forms sidewalls for both the first and second chambers. The first chamber, which is vertically compressed in comparison to those of the Witter and Oh devices, comprises: the upper sidewall of the vessel; a flat, round lid; and a baffle coaxially suspended below the lid by spacers approximately three inches long. The baffle has a perimeter comprising two arc segments having different radii. The larger radius is equal to the inside radius of the vessel and extends for 120-degrees of the baffle's perimeter thereby forming a seal between the baffle and the first chamber's wall for this arc distance. The smaller radius is 1⅛ inch smaller than the larger radius and extends the remaining 240-degrees thereby forming an opening for this arc distance between the baffle and the first chamber's wall. The lid is somewhat larger than the upper rim of the vessel and rests thereon. The lid has a centrally positioned output port for the purpose of attaching a first flexible conduit to a vacuum source. The lid also has a tangentially positioned input port comprising a 90-degree elbow. One end of the elbow protrudes above the lid for the attachment of a second flexible conduit that would go to a debris source. The other end of the elbow is situated between the lid and baffle in a tangential orientation to the both the vessel wall and the upper surface of the larger radius portion of the baffle.
In use, a vacuum source connected via the first flexible conduit creates a suction that draws in debris through the input port via the second flexible conduit from the debris source. The incoming air/debris is then directed tangentially along the walls of the first chamber in a cyclonic manner and most of the debris eventually falls, solely by gravity, into the second chamber through the 240-degree opening. The walls of the vessels are either cylindrical or sloped slightly downward and inward as is the case with many trashcans and pails. Therefore the path of the incoming airflow is circular or may even have an upward bias in the instance where the container walls are sloped. In either case, since the debris is often of small size and low specific gravity, its presence in the first chamber is prolonged making it more susceptible to being drawn into the outlet port.
The Witter, Oh, Thien and other prior-art devices have a common deficiency. They rely solely on the force of gravity to overcome the force of a vortex of air swirling to the outlet. And since the debris is often of small size and low specific gravity some dwells below the outlet for sufficient time that it is drawn by the vortex into the outlet and not collected as intended.
Accordingly, there is a need in the art for a device of simple design that employs a force in addition to gravity to rapidly separate, remove and collect debris from airflow.